Motor and gearbox combination

ABSTRACT

The motor and gearbox combination is for use in a portable power tool having a motor section and a gearbox section. The motor section comprises a motor housing having a first end and an open second end, a first bearing supported at the first end of the motor housing, a stator fixed to the motor housing, a cap closing the open second end of the motor housing and supporting a second bearing and a motor shaft journalled at one end in the bearing and at the other end in the bearing, and a rotor mounted on the motor shaft in confrontation with the stator. The gearbox section comprises a gearbox housing accommodating a gear train and an output shaft. The cap is connected to the gearbox housing at or adjacent to the first end of the motor housing and encloses or substantially encloses the motor housing.

CROSS REFERENCE TO RELATED PUBLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on British Patent Application No. 0229969.1 filed on Dec. 21, 2002.

INTRODUCTION

This invention relates to a motor and gearbox combination for use in a portable power tool and more particularly, but not necessarily, for use in a portable hand held drill.

Portable hand held tools such as drills are driven by electric motors, either battery or mains powered. To increase the output torque of the drill, the motor drives the chuck through a speed reduction gear train. To keep the drill compact and for maximum drilling force, epicyclic gear boxes are preferred.

Conventionally, drill manufacturers have received a motor and a separate gearbox complete with an output shaft. The motor and gearbox have been connected together using a special adaptor plate and then the combined motor and gearbox has been assembled into the casing of the drill. This approach has worked well in aligning the motor to the gearbox but there has been little room for reducing the overall length of the drill as desired by current market trends.

The present invention seeks to provide a compact and reliable motor and gear box combination.

SUMMARY OF THE INVENTION

According to the invention, there is provided a motor and gearbox combination for use in a portable power tool, having:

a motor section comprising:

a motor housing having a first end and an open second end,

a first bearing supported at the first end of the motor housing,

a stator fixed to the motor housing,

a cap closing the open second end of the motor housing and supporting a second bearing,

a motor shaft journalled at one end in the first bearing and at the other end in the second bearing, and a rotor mounted on the motor shaft in confrontation with the stator,

a gearbox section comprising:

a gearbox housing accommodating a gear train and an output shaft characterised in that the cap is connected to the gearbox housing and the cap and gearbox housing enclose the motor housing.

Preferably, the cap extends over the motor housing and is connected to the gearbox housing at or adjacent to the first end of the motor housing.

Preferably, the motor is a PMDC motor having a permanent magnet stator and a wound rotor including a commutator, and the cap supports brush gear in contact with the commutator.

Alternatively, the motor may be a brushless D.C. motor or a universal type motor.

Advantageously, the gear train is an epicyclic gear train. In this case, the epicyclic gear train, preferably, is a two-stage planetary gear system comprising a first sun gear connected to the motor shaft, a first carrier plate, a ring gear surrounding the carrier plate, a plurality of first planet gears in mesh with the first sun gear and the ring gear and supported by the first carrier plate for driving the first carrier plate, a second sun gear connected to the first carrier plate, a second carrier plate and a plurality of second planet gears in mesh with the second sun gear and the ring gear and supported by the second carrier plate for driving the second carrier plate.

The ring gear may be formed as a metallic sleeve which is pressed into the gearbox housing or the gearbox housing could be a moulded part of synthetic resin and the teeth of the ring gear could be moulded directly onto the gearbox housing.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly sectional side view of a preferred embodiment of a motor and gearbox combination according to the present invention, and

FIG. 2 is an exploded perspective view of the motor and gearbox combination shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the motor and gearbox combination shown therein is suitable for use in a hand held power tool such as a drill or electric screwdriver. The combination has a compact overall length. The combination can be divided into two sections, namely a motor section 11 and a gearbox section 12 which includes an output section 13.

The motor section 11, shown on the right, incorporates a D.C. motor having a permanent magnet stator and a wound rotor. The rotor has a shaft 14, a rotor core 15 and a commutator 16 fitted to the shaft 14, with rotor winding 17 wound around the rotor core 15 and terminated on the commutator 16.

The stator has permanent magnets 18 disposed inside a deep drawn motor housing 19 having a first end supporting a bearing 20 and an open second end. A flux ring in the form of a sleeve 21 may, as shown, extend externally around the housing 19. A cylindrical moulded synthetic resin cap 22 closes the open second end of the motor housing 19 and is a sliding fit over the motor housing 19 to which it is keyed by elongate ribs 22 a (see FIG. 2) on the cap 22 and slots in the open end of the housing 19. The end of the cap 22 supports a bearing 23, brush gear 24 and motor terminals 25. The bearing 23 is a self-aligning oil impregnated sintered bronze bushing in which one end of the rotor shaft 14 is journalled. The other end of the rotor shaft is journalled in the bearing 20.

The gearbox section 12 has a gearbox housing 26 which is directly connected by bolts 45 to the open end of the cap 22 at or adjacent to the first end of the motor housing 19. The gearbox housing 26 accommodates a gear train and extends into the output section 13 to support output shaft 27. The gear train is a double or two stage planetary gear type speed reduction gear train.

The cap 22 and gearbox housing 26 are formed of moulded synthetic resin material.

Each stage has a gear carrier 28, 29 which supports three planet gears 30, 31 respectively on spigots 32, 33 respectively. The three first stage planet gears 30 engage a first sun gear 34 in the form of a pinion on the motor shaft 14 and also engage teeth formed on the inner wall of a separate ring gear 35 formed as a metallic sleeve pressed into the housing 26 (as shown) or formed directly on an inner wall of the gearbox housing. Thus, when the motor turns, the pinion or sun gear 34 drives the first planet gears 30 around the inner wall of the housing 26, in turn rotating the first gear carrier 28 via first spigots 32. To the left of the first stage planetary gear is the second stage planetary gear. Again, the second stage planet gears 31 engage a second sun gear 36 and the teeth formed on the inner wall of the gearbox housing 26. The second sun gear 36 is fixed to the rear surface of the first carrier 28 for rotation therewith. The output shaft 27 is fixed to the rear surface of the second carrier 29 for rotation therewith and is supported by a long bushing 37 pressed into the left hand end of the gearbox housing 26. A thrust bearing assembly 38 is located between the bushing 37 and a retaining ring 39 fitted to a circumferential groove in the output shaft 27 to accept thrust loading applied to the output shaft 27.

The motor shaft 14, output shaft 27 and the first and second sun gears 34 and 36 are all co-axial. A washer 40 is placed between the long bushing 37 and the second carrier 29. A second washer 41 is placed between the ring gear 35 and the closed end of the motor housing 19.

Conventionally, the motor and gearbox combination is also provided with a torque spring 42, clutch cap 43 and mounting plate 44. A hammer mechanism could also be included.

The combined motor and gearbox described above is axially compact making it possible for the power tool manufacturers to make shorter and lighter tools.

Although a PMDC motor has been described, other types of motor such as brushless D.C. motors, universal motors and other A.C. motors may be used by suitable adaptation of the motor parts involved.

The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims. For example, the gearbox could be a one-stage or a three-stage gearbox and a three-stage gearbox may provide a three-speed gear train. 

1. A motor and gearbox combination for use in a portable power tool, having: a motor section comprising: a cylindrical deep drawn motor housing having an integrally formed first end and an open second end, said first end being closed except for an opening, a first bearing supported at the first end of the motor housing in said opening, a stator fixed to the motor housing, wherein the motor housing encloses a majority of an axial length of said stator, a cap closing the open second end of the motor housing and supporting a second bearing, said cap enclosing a majority of an axial length of said motor housing, a motor shaft journalled at one end in the first bearing so as to close said first end of said motor housing and at the other end in the second bearing, and a rotor mounted on the motor shaft in confrontation with the stator, a gearbox section comprising: a gearbox housing accommodating a gear train and an output shaft, the first end of said motor housing being adjacent said gear box section, the cap being directly connected to the gearbox housing and the cap and gearbox housing substantially enclosing the motor housing.
 2. The combination of claim 1, wherein the motor is a PMDC motor having a permanent magnet stator and a wound rotor including a commutator and the cap supports a brush gear in contact with the commutator.
 3. The combination of claim 1, wherein the motor is a brushless D.C. motor.
 4. The combination of in claim 1, wherein the motor is a universal type motor.
 5. The combination of claim 1, wherein the gear train is an epicyclic gear train.
 6. The combination of claim 5, wherein the epicyclic gear train is a two stage planetary gear system comprising a first sun gear connected to the motor shaft, a first carrier plate, a ring gear surrounding the carrier plate, a plurality of first planet gears in mesh with the first sun gear and the ring gear and supported by the first carrier plate for driving the first carrier plate, a second sun gear connected to the first carrier plate, a second carrier plate and a plurality of second planet gears in mesh with the second sun gear and the ring gear and supported by the second carrier plate for driving the second carrier plate.
 7. The combination of claim 6, wherein the ring gear is formed as a metallic sleeve which is pressed into the gearbox housing.
 8. The combination of claim 6, wherein the gearbox housing is a moulded part of synthetic resin and the teeth of the ring gear are moulded directly onto the gearbox housing.
 9. The combination of claim 1, further comprising a washer between said first end of said motor housing and said gear box train.
 10. A motor and gearbox combination for use in a portable power tool, having: a motor section comprising: a cylindrical deep drawn motor housing having an integrally formed first end and an open second end, said first end being closed except for an opening, a first bearing supported at the first end of the motor housing in said opening, a stator fixed to the motor housing, wherein the motor housing enclosed a majority of an axial length of said stator, a cap closing the open second end of the motor housing and supporting a second bearing, said cap enclosing a majority of an axial length of said motor housing. a motor shaft journalled at one end in the first bearing so as to close said first end of said motor housing and at the other end in the second bearing, and a rotor mounted on the motor shaft in confrontation with the stator, a gearbox section comprising: a gearbox housing accommodating a gear train and an output shaft, the first end of said motor housing being adjacent said gear box section, the cap being directly connected to the gearbox housing and the cap and gearbox housing substantially enclosing the motor housing: wherein the cap extends over the motor housing and is connected to the gearbox housing at or adjacent to the first end of the motor housing. 